156 DIFCO MANUAL 



containing crystal violet and sodium azide as a selective broth in the isolation of 

 mastitis streptococci. Hartman^ reported the value of sodium azide as a selective 

 agent for the isolation of streptococci causing mastitis. Bryan, Devereux, Hirschey 

 and Corbett^ reported that sodium azide in a concentration of 1 : 5,000 was a 

 better selective preservative for milk cultures and gave more accurate results for 

 the microscopic and Hotis tests for Streptococcus mastitis than 1 : 50,000 brilliant 

 green. Snyder and Lichstein* and Lichstein and Snyder^ reported that sodium 

 azide in 0.01 per cent concentration in blood agar prevented the swarming of 

 proteus, and permitted the isolation of streptococci from known mixtures of 

 bacteria. The common Gram-negative bacteria were inhibited on this medium. 

 Packer^ modified Edwards' medium and prepared an Infusion Blood Agar con- 

 taining 1 : 15,000 sodium azide and 1 : 500,000 crystal violet for the study of bovine 

 mastitis and recommended it as a selective medium for the cultural examination 

 of pathogenic streptococci from human sources. 



Mallmann, Botwright and Churchill" in studying the selective bacteriostatic 

 effect of slow oxidizing agents reported that sodium azide exerted a bacteriostatic 

 effect on Gram-negative bacteria and permitted the growth of Gram-positive 

 organisms. Packer^ used 1:15,000 sodium azide and 1:500,000 crystal violet in 

 a Blood Agar prepared with 1.5 per cent Bacto-Tryptose for the selective isola- 

 tion of Erysipelothrix rhusiopathiae. "Standard Methods for the Examination of 

 Dairy Products"^ specifies the use of sodium azide in agar media prepared with 

 Bacto-Tryptose for the isolation of pathogenic bacteria from cheese. 



Sodium azide has also been used in liquid media for the detection of fecal 

 streptococci in stools, sewage, swimming pools and drinking water supplies. See 

 Bacto-S F Medium, page 46, Bacto-B A G G Broth, page 47, and Bacto-Azide 

 Dextrose Broth, page 48 for the discussion of these media. 



To rehydrate the medium, suspend 33 grams of Bacto-Azide Blood Agar Base 

 ia 1000 ml. of cold distilled water and heat to boiling to dissolve the medium 

 completely. Distribute in tubes or flasks and sterilize in the autoclave for 15 

 minutes at 15 pounds pressure (121°C.). In the preparation of Azide Blood 

 A.gar, cool the sterile melted medium to 45-50°C. and add 5 per cent sterile 

 defibrinated blood, under aseptic conditions. Distribute in tubes or flasks. 



One pound of Bacto-Azide Blood Agar Base will make 13.7 liters of medium. 



i J. Comp. Path. Therap., 46:211:1933. « J. Bact., 42:138:1941. 



3 Milchw. Forsch., 18:116:1936. ' J. Infectious Diseases, 69:215: 1941. 



3 North Am. Vet., 20:424:1939. * J. Bact., 46:343:1943. 



* J. Infectious Diseases, 67:113:1940. 8 Standard Methods for the Examination of 



^}. Bact., 42:653:1941. Dairy Products, 9th Edition: 165: 1948. 



Differential Liquid Enrichments 



The use of selective enrichment media is a recommended procedure for aiding 

 in the isolation of Salmonella. Preliminary inoculation of the suspected sample 

 into liquid enrichments, followed by incubation for 18 hours before inoculation 

 on suitable plating media, materially increases the percentage of isolations of 

 Salmonella. 



